The teens were part of crowd that grew to 200, police say. Most were students, who came into Center City after school. A fight broke out first between two girls at 15th and Chestnut, and then escalated into a full-out brawl.

"Once the weather breaks it starts to break out," said Drew Carballo, the manager of Del Frisco's restaurant, who witnessed the chaos.

Tuesday was the warmest day the city has seen in seven months, according to NBC10 Chief Meteorologist Glenn "Hurricane" Schwartz. The high was a record-tying 84 degrees in Philadelphia. The last time it was that hot was on September 22, 2012.

"We do not tolerate the type of behavior exhibited yesterday afternoon and it is not an accurate reflection of our Catholic values," said Kenneth A. Gavin, Director of Communications for the Archdiocese of Philadelphia in a statement. Gavin said students from other Catholic high schools were also part of the crowd.

Students who were arrested will face disciplinary action, according to Gavin. He also asked for anyone with information on the brawl to contact Philadelphia police.

In addition to the three seniors from Bishop McDevitt, another 18-year-old, Mitchell Symeir, was charged with the same crimes. He is a senior at Overbrook High. Charges were filed against 10 juveniles today as well, but no information is being released on their cases because they are minors.

Tuesday's flash-mob fight was one of two brawls in the city and both began with fights between girls.

The second melee, however, which took place in Kensington, ended violently. A gunman opened fire, killing an 18-year old girl who had come from around the block to see what all the commotion was about. Three other people were shot .

In that melee, police say the crowd grew to 75 or 100 people. A search is on tonight for the gunman.